1. Field of the Invention
The present invention relates to an impedance detection device and, more particularly, to a minute impedance variation detection device.
2. Description of Related Art
Generally, the existed touch panels can be classified into resistive type and capacitive type. The resistive touch panels have been developed much earlier than others and thus occupy the major market, while the capacitive touch panels are also in widespread use recently.
The resistive touch panel is formed by stacking an upper ITO (Indium Tin Oxide) conductive layer and a lower ITO conductive layer. In actual operation, the pressure applied to the surface of the resistive touch panel makes the electrode of the upper conductive layer to be conducted with the electrode of the lower conductive layer, and a controller is employed to detect the voltage variation of the touch panel so as to compute the position of the contact point thereby to proceed as an input. When a user touches a certain point on the surface of the touch panel, current flows conducted makes an activation, and the controller therefore computes the position of the activated point. However, for the touch panel with such a dual-layer ITO structure, the layer gap for connecting ITO electrodes on the same plane is relatively narrow, and thus it is likely to cause short circuit problem, resulting in detection errors.
Furthermore, in the development of the capacitive touch panel, the major factors that affect the self-capacitance are the electric field of human body and the contact area, in which the electric field of human body typically carries signals due to the influence of the electric field of earth. In order to effectively reduce the influence of the electric field of human body, the measurement circuit generally applies the mean value to compute the capacitance value. That is, the mean value of the capacitance values computed for multiple times is taken to determine whether there is a touch input. Therefore, if the electric field of human body and the electric field of earth are treated as noises, the accuracy and stability of the capacitive touch panel are greatly influenced.
Accordingly, in use of the aforementioned touch-control device, it is difficult to avoid the influence of noises from circuit, electric field, power source, etc. In addition, based on the consideration of accuracy and stability, ITO electrodes with smaller resistance value are typically used in the aforementioned touch-control device, and thus it is difficult to manufacture large-sized touch panel, resulting in a restriction of developing the touch panel.